Code Geass: Hangyaku no Lelouch - Lost Stories

Area 11, or Japan, is occupied by the superpower, the Holy Britannian Empire. Two boys live there: Mario Diesel and Lelouch Lamperouge. While Japanese people are oppressed as Elevens, Mario lives his school life hiding the fact that he is half Britannian and half Japanese. Lelouch lives his days as the vice president of the school's student council, hiding his true identity as the prince of Britannia. The destinies of these two people who never crossed paths intersect due to a certain incident, and a story of revenge and rebellion begins.

(Source: JumpToon, translated)